1. Field
Embodiments of the present invention relate to a method and apparatus for determining registration error of patterns applied to a strip of material by a rotary die.
2. Related Art
It is known in a variety of industries to implement a manufacturing technique that involves die cutting, embossing, or stamping a series of patterns on a continuous strip of material or web of material by passing it between a pair of cooperatively rotating rotary die cylinders. This technique may be used, for example, to cut holes onto a printed strip of material at desired locations relative to indicia printed thereon. When the patterns are positioned at specific locations relative to each other or relative predetermined indicia, the patterns are said to be “in registration.”
A controller or other control device may be used to achieve registration. The controller maintains a die cut at the same interval as the repeat of patterns and/or indicia on the strip of material. To line up the die and patterns printed on the strip of material, the operator offsets a registration target position, which shifts the die patterns up or down the strip of material, effectively lining up the intervals of the strip of material and the die. However, over the course of die cutting the entire length of the strip of material, the strip of material can slip out of alignment with the rotary die. If one of the patterns is not positioned precisely at the desired location on the strip of material, the amount of offset between the two may be referred to as “registration error”. One type of registration error may occur in the machine direction, or in the direction of movement of the strip of material.
Manual methods for determining a registration error for each pattern applied to the strip of material are too time-consuming for mass production operations. Prior art automated methods of measuring and calculating registration error for each pattern applied by the rotary die involve complex and/or numerous equations and compare statements, which can slow the processing time and the processing capability needed to determine the registration error and correct for this registration error “on the fly” or in a substantially continual manner for each pattern.
Accordingly, there is a need for a method and apparatus for determining a registration error that overcomes the limitations of the prior art.